Rock bolts are used extensively in underground mining. The type of rock bolt which is used, and the way it is used, are determined by various factors including geological conditions at an installation site.
When a relatively narrow seam of ore is mined, it is cost-effective to remove only sufficient rock to enable the seam to be accessed by workers. This aspect, at least, can give rise to relatively narrow stopes which may be no more than 900 mm in height. Conditions in this type of excavation are arduous and can be daunting. Safe mining in this kind of environment requires that the rock body must be adequately supported.
Various support techniques can be used. In one approach, e.g. in hard rock mining in South African gold mines, a relatively large diameter hole is drilled into a rock body and thereafter a rock bolt is inserted into the hole. A point anchor can be used to fix the bolt in place but, preferentially, full column grouting is used to obtain superior load characteristics. To achieve this objective, without making excessive use of steel, a tubular steel rock bolt, as opposed to a solid steel shank, is inserted into a hole and fixed in position using a grout or a resin mix. This technique provides good support and is well-established and, for this reason, is not further described herein.
In a narrow stope of, say, 900 mm, it may be a requirement, to achieve satisfactory levels of operation, for each rock bolt to extend into the rock body by, for example, 1800 mm. If the rock bolt is made from a rigid tubular member then this aspect can only be adequately addressed if a bolt is made from relatively short segments which can be handled in a narrow stope and which can be assembled, as required, during the installation process.
An object of the present invention is to provide a rock bolt which can be assembled at an underground site from relatively small tubular sections, without compromising the strength of the assembled rock bolt and which allows for effective full column grouting or resin fixing.